Molecular typing of VapA-positive Rhodococcus equi isolates from Jeju native horses, Korea

We recently demonstrated the presence of virulence-associated protein antigen (VapA)-positive Rhodococcus equi in Jeju Island, Korea. These bacteria contained one of two distinct plasmid types, a 90-kb type II plasmid, which has been found in isolates from the native Kiso horses of Japan, and a new variant, a 90-kb type V plasmid. However, the genotypic characters of the VapA-positive R. equi from Jeju native horses and their environments are poorly understood. Ninety-eight isolates from soil samples and 89 isolates from fecal samples were collected from five farms that breed or have bred Jeju native horses, and were tested for the presence of VapA by immunoblotting and PCR. Of the 98 soil isolates and 89 fecal isolates, seven and 13 were VapA-positive R. equi, respectively. In 2003, two Jeju foals died suddenly and were brought to the Faculty of Veterinary Medicine, Cheju National University, for postmortem examination. Pure cultures of R. equi were isolated from the lung lesions of both foals. Of the 16 clinical isolates, 14 were VapA-positive R. equi. Of the 34 VapA-positive clinical and environmental isolates, 16 contained the 90-kb type II plasmid and 18 contained a 90-kb type V plasmid. Pulsed-field gel electrophoresis (PFGE) patterns of the VapA-positive isolates from Jeju horses and Kiso horses, containing the 90-kb type II plasmid, were compared and formed two distinct groups. Furthermore, 18 virulent isolates containing the 90-kb type V plasmid formed two distinct PFGE groups (of 16 and two isolates). These results demonstrate that two virulence plasmid types are widespread in R. equi in Jeju native horses. However, there is little diversity in the PFGE patterns of virulent isolates, suggesting the clonal spread of virulent R. equi. The PFGE pattern of the virulent R. equi isolates from Jeju native horses in Korea is not identical to those of Kiso native horses in Japan.     

Isolation of virulent Rhodococcus equi from native Japanese horses

R. equi was isolated from soil samples obtained from the environment of seven native Japanese horse breeds (Hokkaido, Kiso, Noma, Misaki, Tokara, Miyako and Yonaguni) and from fecal samples collected from three native horse breeds (Hokkaido, Kiso and Misaki). Virulent R. equi at various levels (ranging from 0.5 to 12.9%) was isolated from the feces or soil environment of Hokkaido, Kiso and Misaki horses. Isolates were investigated both for the presence of 15- to 17-kDa antigens (virulence-associated protein antigens; VapA) by colony blotting, using the monoclonal antibody 10G5, and the gene of VapA by PCR. Plasmid DNAs extracted from positive isolates were digested with restriction endonucleases, and the digestion patterns of the plasmids of virulent isolates were divided into three types. Two of the three types (87-kb type II and 90-kb type I) had already been reported in Japanese isolates, and a new type (tentatively designated as 90-kb type II) had been found in isolates from Kiso horses. Six virulent R. equi isolates from the Hokkaido horses contained an 87-kb type II plasmid. Eight of 24 isolates from the Kiso horses contained an 87-kb type II plasmid, and the remaining 16 contained a 90-kb type II (a new type) plasmid. Two isolates from the Misaki horses contained a 90-kb type I plasmid. These results demonstrate the geographic difference in the distribution of virulence plasmids in R. equi isolates among native Japanese horses.     

Isolation of Rhodococcus equi from the feces of indigenous animals and soil from the Lower Zambezi National Park and Lochinvar National Park, Zambia

Rhodococcus equi is an important pathogen in foals; however, its incidence in African indigenous animals is poorly understood. Fecal samples (92 from nine indigenous species) and 43 soil samples were collected from two Zambian National Parks. The presence of R. equi was investigated and 533 isolates were tested for the presence of 15- to 17-kDa antigens (VapA) and a 20-kDa antigen (VapB) by immunoblotting and PCR. R. equi was isolated (10(2)-10(4) colony forming units/g) from 75% of fecal and 74% of soil samples. Neither antigen was detected; however, about 20% of the isolates contained cryptic plasmids of various sizes. There was no evidence of virulent R. equi, but the avirulent form was widespread in the animals and the soil.     

中国内蒙自治区马饲育环境土壤中马红球菌的分布

对中国内蒙古自治区饲育马土壤环境中马红球菌的分布知之甚少;为此,在中国内蒙古通辽近郊、内蒙古南部锡林郭勒盟大草原、内蒙古东部呼伦贝尔大草原等马场共收集了108份土壤样品进行了马红球菌的检测。结果,锡林郭勒盟大草原和呼伦贝尔大草原的马红球菌分离率为25.9%～30.0%,通辽近郊土壤中分离率高达82.3%。这说明在通辽近郊马红球菌的分离菌数是草原土壤中马红球菌分离菌数的10倍。应用PCR技术检测了488株的毒力相关基因,相对分子质量分别为15000～17000（VapA）和20000（VapB）。所有的分离株都未检出毒力相关基因。这些无毒力分离株的质粒资料显示,各种大小的潜在质粒的发生率为13.3%～21.5%。本研究结果截然不同于我们新近对蒙古国的调查结论：马红球菌在蒙古国乌兰巴托的马群中不存在。造成这一差异的原因可能在于蒙古国的游牧生活和内蒙古的非游牧生活。     

Rhodococcus equi in the soil environment of horses in Inner Mongolia, China

Little is known about the distribution of Rhodococcus equi in the soil environment of native horses in China. One hundred and eight soil samples were collected from native-horse farms in the Hulun Beier grasslands of eastern Mongolia, the Xilin Goler grasslands of southern Mongolia, and Tongliao City in Inner Mongolia, China. The isolation rates of R. equi from soil samples from the Hulun Beier and Xilin Goler grasslands ranged from 25.9% to 30.0%. In contrast, isolation rates from soil samples from Tongliao City were as high as 82.3% and the mean number of R. equi in soil samples from Tongliao City was 10 times more than those of samples from the grasslands. The 488 isolates were examined using PCR for the presence of genes that encode virulence-associated 15-17 kDa antigen protein (VapA) and the 20 kDa antigen protein (VapB). All isolates were negative for virulence-associated proteins. Plasmid profiles of these avirulent isolates showed that cryptic plasmids of various sizes were present with an incidence of 13.3% to 21.5%. The results of the present study contrast with those of our recent study (J. Vet. Med. Sci. 67:611-613, 2005), in which we reported that R. equi was absent from Mongolian horses in Ulaanbaatar, Mongolia. It is suggested that the difference between the results of these two studies is due to the mobile pasturing system in Mongolia and nonmobile pasturing system in Inner Mongolia.     

Rhodococcus equi in fecal and environmental samples from Kansas horse farms

Horse farms in Kansas were surveyed for the incidence of Rhodococcus equi. Fecal specimens and soil or cobweb samples were collected from each farm and cultured on selective media. One control farm (with no history of R. equi infection), one farm which had an outbreak 3 and 4 years previously and 2 farms which had R. equi-infected foals that season were surveyed. In addition, fecal samples from 21 horses hospitalized in the Kansas State University Veterinary Hospital were cultured. There was no significant difference in the incidence of R. equi in fecal samples from the 2 farms with recent disease problems. The farm with a history of disease had a significantly higher percentage of positive fecal cultures than the 2 farms with a more recent history of disease. Neither ration composition nor sex of the horses appeared to affect the fecal culture results. Fecal samples from 2 birds on 1 farm were positive for R. equi.     

Prevalence of virulent Rhodococcus equi in isolates from soil collected from two horse farms in South Africa and restriction fragment length polymorphisms of virulence plasmids in the isolates from infected foals, a dog and a monkey

The prevalence of virulent Rhodococcus equi in soil isolates from two horse farms in South Africa and nine clinical isolates from six foals, a foal foetus, a dog, and a monkey was investigated. The isolates were tested for the presence of virulence plasmid DNA and 15- to 17-kDa antigens by immunoblotting. Rhodococcus equi was isolated from almost all of the soil samples obtained from the two farms with 5.0 x 10(1) to 3.3 x 10(4) colony forming units per gram of soil. Virulent R. equi was isolated from three soil samples from one of the farms and appeared in 3.8% (three of 80 isolates), but not in any of the 182 isolates from the other farm. Of the three virulent R. equi isolates, one contained an 85-kb type I plasmid and two an 87-kb type I plasmid. Of nine clinical isolates from the foals, foal foetus, dog and monkey, five from the foals were virulent R. equi which expressed the virulence-associated antigens and contained a virulence plasmid 85-kb type I, and were all isolated from cases of pneumonia typical of that induced by R. equi in young foals living in widely separated areas in South Africa. The isolates from the other four foals, the dog and the monkey were avirulent R. equi.     

Rhodococcus equi virulence plasmids recovered from horses and their environment in Jeju, Korea: 90-kb type II and a new variant, 90-kb type V

Rhodococcus equi was isolated from fecal and soil samples from four native Jeju horse farms and six Thoroughbred farms in Jeju, Korea. The isolates were examined for the presence of virulence-associated 15-17-kDa antigens (VapA) by colony blotting, using the monoclonal antibody 10G5, and for the gene encoding VapA by PCR. R. equi was isolated from all 36 soil samples collected from the 10 farms with between 5.0 x 10(2) and 7.5 x 10(4) colony-forming units (cfu) per gram of soil, and from 37 of 40 fecal samples with between 5.0 x 10(1) and 1.1 x 10 (5) cfu per gram of feces. Virulent R. equi was isolated from seven farms and appeared in 2.0% of isolates (10 of 508). Of the 10 virulent isolates, four contained a 90-kb type II plasmid, which has been found in isolates from the Kiso native horses of Japan, and the other six contained a new variant, which did not display the EcoRI and EcoT22I digestion patterns of the 10 representative plasmids already reported (85-kb types I, II, III, and IV; 87-kb types I and II; 90-kb types I, II, III, and IV). We designated the new variant as the "90-kb type V" plasmid, because its EcoRI digestion pattern is similar to that of the 90-kb type II plasmid. This is the first report of the prevalence of virulent R. equi in Jeju, Korea. The same virulence plasmid type is found in both Korean and Japanese isolates, providing insight into the origin, ancestry, and dispersal of native horses in Korea and Japan.     

Pathologic findings in reintroduced Przewalski's horses (Equus caballus przewalskii) in southwestern Mongolia.

The Przewalski's horse (Equus caballus przewalskii) was extinct in the wild by the mid 1960s. The species has survived because of captive breeding only. The Takhin Tal reintroduction project is run by the International Takhi Group; it is one of two projects reintroducing horses to the wild in Mongolia. In 1997 the first harem group was released. The first foals were successfully raised in the wild in 1999. Currently, 63 Przewalski's horses live in Takhin Tal. Little information exists on causes of mortality before the implementation of a disease-monitoring program in 1998. Since 1999, all dead horses recovered (n = 28) have been examined and samples collected and submitted for further investigation. Equine piroplasmosis, a tick-transmitted disease caused by Babesia caballi or Theileria equi, is endemic in Takhin Tal and was identified as the cause of death of four stallions and one stillborn foal. In December 2000, wolf predation was implicated in the loss of several Przewalski's horses. However, thorough clinical, pathologic, and bacteriologic investigations performed on dead and surviving horses of this group revealed lesions compatible with strangles. The extreme Mongolian winter of 2000-2001 is thought to have most probably weakened the horses, making them more susceptible to opportunistic infection and subsequent wolf predation. Other occasional causes of death since 1999 were trauma, exhaustion, wasting, urolithiasis, pneumonia, abortion, and stillbirth. The pathologic examination of the Przewalski's horses did not result in a definitive diagnosis in each case. Several disease factors were found to be important in the initial phase of the reintroduction, which could potentially jeopardize the establishment of a self-sustaining population.     

Genotypic characterization of VapA positive Rhodococcus equi in foals with pulmonary affection and their soil environment on a warmblood horse breeding farm in Germany

Pulsotypes of VapA positive Rhodococcus equi isolated from foals and soil on a farm in Germany were characterized on the basis of nasal and tracheal samples simultaneously collected in 2003 from 217 foals with sonographic evidence of pneumonia or pulmonary abscesses. Of the 217 double samples, R. equi was isolated in 118 (54%) of the tracheal samples and in 52 of the nasal swab samples (24%) (P<0.001). Furthermore, 37 and 55 isolates were also randomly selected from nasal swabs and the tracheal samples, respectively, and further processed to determine the presence of VapA by colony blot enzyme-linked immunosorbent assay. This method showed that 26 (68%) of the nasal swabs and 40 (73%) of the tracheal samples were VapA-positive. R. equi was isolated from 56 (87%) of the 64 soil samples taken from the paddocks and stables in March and from 17 (68%) of the 25 samples taken in July of 2003. Three (21%) of these randomly selected 14 isolates from March and 13 (81%) of the 16 from July were VapA-positive. The VapA positive isolates from foals and soil were genotyped by plasmid profiling, restriction fragment length polymorphism analysis and pulsed-field gel electrophoresis. Of the 83 isolates, 80 contained an 85-kb type I plasmid and three contained an 87-kb type I plasmid. Pulsed-field gel electrophoresis yielded four distinct VspI profiles dividing 83 isolates into three major (A1, 51; D, 14; and 11 isolates) and three minor (C, 4; A3, 2; and A2, 1 isolates) groups. These results suggest that the majority of foals were exposed to and infected with three pulsotypes of VapA positive R. equi containing an 85-kb type I plasmid.     

The association between weather, frenzied behaviour, percutaneous invasion by Strongyloides westeri larvae and Rhodococcus equi disease in foals

Episodes of frenzy lasting approximately 30 minutes were observed among horses confined to enclosures surfaced with sand or soil. The probability of sighting these episodes increased by a factor of three when within 24 hours there was 0.2mm or more of rain, a maximum air temperature between 16.7 - 26.6 degrees C and a soil temperature of 16.3 - 23.9 degrees C at 30 cm. High egg counts of Strongyloides westeri appeared in faeces four to five days later and persisted for several days. Rhodococcus equi was recovered from all soil samples, and from the faeces of 76% of mares and 82% of foals. The youngest foal was five days old when the organism was isolated from rectal faeces. In contrast to the majority of reports, the lesions of R. equi in the foals were confined to limbs and peripheral lymph nodes. It is proposed that the percutaneous invasion of these foals by third stage larvae of S. westeri facilitated invasion of R. equi, and ubiquitous saprophytic opportunist pathogen.     

Prevalence of virulent Rhodococcus equi in soil from five R. equi-endemic horse-breeding farms and restriction fragment length polymorphisms of virulence plasmids in isolates from soil and infected foals in Texas.

Rhodococcus equi isolates (462) obtained from 64 soil samples collected on 5 R. equi-endemic horse-breeding farms and isolates from 100 infected foals in Texas were examined to determine the prevalence and genotypic diversity of virulence-associated plasmids. Isolates were tested for the presence of 15-17-kDa virulence-associated protein antigens (VapA) by immunoblotting and virulence-associated plasmids by PCR. Plasmid DNAs were isolated and analyzed by digestion with restriction endonucleases for estimation of size and comparison of polymorphisims. Rhodococcus equi were isolated from soil of all 5 farms; however, virulent R. equi were only isolated from 3 of the 5 farms and represented 18.8% (87 of 462) of total isolates. Of the 87 virulent soil isolates, 56 (64.5%) contained an 85-kb type I plasmid, 23 (26.4%) an 87-kb type I plasmid, 7 (8%) a newly defined 85-kb type III plasmid (Tx 43), and 1 (1.1%) a newly defined 85-kb type IV plasmid (Tx 47). Of the 100 isolates from infected foals, 96 were virulent. Of the 96 virulent isolates, 51 (53.1%) contained an 85-kb type I plasmid, 39 (40.6%) an 87-kb type I plasmid, 4 (4.2%) an 85-kb type III plasmid (Tx 43), and 2 (2.1%) an 85-kb type IV plasmid (Tx 47). There are at least 4 different R. equi virulence-associated plasmids in Texas, 2 of which have not previously been described. Based upon virulence plasmid typing, there is geographic diversity among isolates of R. equi from clinical and environmental samples on horse-breeding farms in Texas. There is not a strong correlation between the presence of virulent R. equi in farm soils and the R. equi disease status of those farms.     

Serotypes of Rhodococcus equi isolated from horses, immunocompromised human patients and soil in Hungary

Two hundred and twelve Rhodococcus equi strains were isolated from soil, nasal and rectal swabs of horses and immunocompromised human patients in Hungary and serotyped using Prescott's serotyping system. One hundred and forty-seven strains (69.3%) belonged to serotype 1, 22 strains (10.4%) to serotype 2, 6 strains (2.8%) to serotype 3 and 1 strain (0.5%) to serotype 4. Serotypes 5, 6 and 7 were not found and 36 strains (17%) could not be typed. Serotype 1 (72%) was the type most commonly isolated from clinical samples of foals or from the soil of horse facilities. Six out of 8 R. equi strains from humans belonged to serotype 2, and two human strains were untypable. The data show that the prevalence of R. equi serotypes varies in different geographic areas of the country.     

Association of soil concentrations of Rhodococcus equi and incidence of pneumonia attributable to Rhodococcus equi in foals on farms in central Kentucky

OBJECTIVE: To determine whether soil concentrations of total or virulent Rhodococcus equi differed among breeding farms with and without foals with pneumonia caused by R equi. SAMPLE POPULATION: 37 farms in central Kentucky. Procedures-During January, March, and July 2006, the total concentration of R equi and concentration of virulent R equi were determined by use of quantitative bacteriologic culture and a colony immunoblot technique, respectively, in soil specimens obtained from farms. Differences in concentrations and proportion of virulent isolates within and among time points were compared among farms. RESULTS: Soil concentrations of total or virulent R equi did not vary among farms at any time point. Virulent R equi were identified in soil samples from all farms. Greater density of mares and foals was significantly associated with farms having foals with pneumonia attributable to R equi. Among farms with affected foals, there was a significant association of increased incidence of pneumonia attributable to R equi with an increase in the proportion of virulent bacteria between samples collected in March and July. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that virulent R equi were commonly recovered from soil of horse breeding farms in central Kentucky, regardless of the status of foals with pneumonia attributable to R equi on each farm. The incidence of foals with pneumonia attributable to R equi can be expected to be higher at farms with a greater density of mares and foals.     

Ecology of Rhodococcus equi in horses and their environment on horse-breeding farms

Quantitative culture of R. equi in the feces of dams and foals, in the air of the stalls and in the soil of the paddocks was carried out on three horse-breeding farms during the foaling season. The isolation rates of R. equi from the feces of dams from the 3 farms suddenly increased to approximately 80% at the end of March, when the snow in the paddocks finished melting, and remained at that level during April and May. The mean number of R. equi and the isolation rate of R. equi from the feces of dams on the farms were investigated for 5 weeks before and 5 weeks after delivery. During the 10 weeks, there were no differences in the isolation rate or in the mean number of R. equi from the feces of dams. R. equi was first isolated from the feces of the foals born in February and the middle of March at 3-4 weeks of age, on the other hand, it was first isolated from the feces of foals born in the end of March and April at 1-2 weeks of age. The number of R. equi in the soil collected from the paddocks used by dams during the winter was approximately 10(2)-10(4) g-1 of soil during the experiment. R. equi was isolated from the air in the stalls at the end of March and the number of R. equi in the air increased particularly on dry and windy days.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chemoprophylactic effects of azithromycin against Rhodococcus equi-induced pneumonia among foals at equine breeding farms with endemic infections

OBJECTIVE: To determine the effect of azithromycin chemoprophylaxis on the cumulative incidence of pneumonia caused by Rhodococcus equi, age at onset of pneumonia, and minimum inhibitory concentration (MIC) of azithromycin for R equi isolates cultured from fecal and clinical samples. DESIGN: Controlled, randomized clinical trial. ANIMALS: 338 foals born and raised at 10 equine breeding farms; each farm had a history of endemic R equi infections. PROCEDURES: Group 1 foals were control foals, and group 2 foals were treated with azithromycin (10 mg/kg [4.5 mg/lb], PO, q 48 h) during the first 2 weeks after birth. Foals were monitored for development of pneumonia attributable to R equi infection and for adverse effects of azithromycin. Isolates of R equi were tested for susceptibility to azithromycin. RESULTS: The proportion of R equi-affected foals was significantly higher for control foals (20.8%) than for azithromycin-treated foals (5.3%). Adverse effects of azithromycin treatment were not detected, and there were no significant differences between groups for the MICs of azithromycin for R equi isolates cultured from fecal or clinical samples. CONCLUSIONS AND CLINICAL RELEVANCE: Azithromycin chemoprophylaxis effectively reduced the cumulative incidence of pneumonia attributable to R equi among foals at breeding farms with endemic R equi infections. There was no evidence of resistance to azithromycin. Nonetheless, caution must be used because it is possible that resistance could develop with widespread use of azithromycin as a preventative treatment. Further investigation is needed before azithromycin chemoprophylaxis can be recommended for control of R equi infections.     

Association of disease with isolation and virulence of Rhodococcus equi from farm soil and foals with pneumonia

OBJECTIVE: To determine whether isolation and virulence of Rhodococcus equi from soil and infected foals are associated with clinical disease. DESIGN: Cross-sectional and case-control study. SAMPLE POPULATION: R equi isolates from 50 foals with pneumonia and soil samples from 33 farms with and 33 farms without a history of R equi infection (affected and control, respectively). PROCEDURE: R equi was selectively isolated from soil samples. Soil and clinical isolates were evaluated for virulence-associated protein antigen plasmids (VapA-P) and resistance to the beta-lactam antibiotics penicillin G and cephalothin. Microbiologic cultures and VapA-P assays were performed at 2 independent laboratories. RESULTS: VapA-P was detected in 49 of 50 (98%) clinical isolates; there was complete agreement between laboratories. Rhodococcus equi was isolated from soil on 28 of 33 (84.8%) affected farms and 24 of 33 (72.7%) control farms, but there was poor agreement between laboratories. Virulence-associated protein antigen plasmids were detected on 14 of 66 (21.2%) farms by either laboratory, but results agreed for only 1 of the 14 VapA-P-positive farms. We did not detect significant associations between disease status and isolation of R equi from soil, detection of VapA-P in soil isolates, or resistance of soil isolates to beta-lactam antibiotics. No association between beta-lactam antibiotic resistance and presence of VapA-P was detected. CONCLUSIONS AND CLINICAL RELEVANCE: On the basis of soil microbiologic culture and VapA-P assay results, it is not possible to determine whether foals on a given farm are at increased risk of developing disease caused by R equi.     

Association of pneumonia in foals caused by Rhodococcus equi with farm soil geochemistry

OBJECTIVE: To quantify and compare geochemical factors in surface soils from horse-breeding farms with horses with pneumonia caused by Rhodococcus equi (affected farms) and horse-breeding farms with no history of pneumonia caused by R equi (unaffected farms). SAMPLE POPULATION: Soil from 24 R equi-affected farms and 21 unaffected farms. PROCEDURE: Equine veterinary practitioners throughout Texas submitted surface soil samples from areas most frequented by foals, on R equi-affected and unaffected horse-breeding farms in their practice. Soil samples were assayed for the following factors: pH, salinity, nitrate, phosphorus, potassium, calcium, magnesium, sodium, sulfur, zinc, iron, manganese, and copper. Median values for all factors were recorded, and differences between affected and unaffected farms were compared. RESULTS: Significant differences in soil factors were not detected between affected and unaffected farms; hence, there was no association between those factors and R equi disease status of the farms. CONCLUSIONS AND CLINICAL RELEVANCE: The surface soil factors monitored in this study were not significant risk factors for pneumonia caused by R equi. As such, it is not possible to determine whether foals on a given farm are at increased risk of developing disease caused by R equi on the basis of these factors. Data do not support altering surface soil for factors examined, such as alkalinization by applying lime, as viable control strategies for R equi.     

Equine humoral immune response to Rhodococcus (Corynebacterium) equi

An enzyme-linked immunosorbent assay was developed to test equine serum for the presence of antibodies to Rhodococcus (Corynebacterium) equi. Experimental ponies had no detectable antibody to R equi before exposure to the bacterium. After experimental inoculation, animals in groups that received live R equi subcutaneously or intranasally/intratracheally developed high titers to R equi. Noninoculated controls remained seronegative. Serum was also collected from horses of various ages that were naturally exposed to R equi. There was a wide range of anti-R equi titers in these horses. Because experimentally infected horses seroconverted when some naturally infected foals did not seroconvert, the function of antibody in resistance to R equi infection remains unknown.     

Evaluation of fecal samples from mares as a source of Rhodococcus equi for their foals by use of quantitative bacteriologic culture and colony immunoblot analyses

OBJECTIVE: To determine whether mares are a clinically important source of Rhodococcus equi for their foals. SAMPLE POPULATION: 171 mares and 171 foals from a farm in Kentucky (evaluated during 2004 and 2005). PROCEDURES: At 4 time points (2 before and 2 after parturition), the total concentration of R equi and concentration of virulent R equi were determined in fecal specimens from mares by use of quantitative bacteriologic culture and a colony immunoblot technique, respectively. These concentrations for mares of foals that developed R equi-associated pneumonia and for mares with unaffected foals were compared. Data for each year were analyzed separately. RESULTS: R equi-associated pneumonia developed in 53 of 171 (31%) foals. Fecal shedding of virulent R equi was detected in at least 1 time point for every mare; bacteriologic culture results were positive for 62 of 171 (36%) mares at all time points. However, compared with dams of unaffected foals, fecal concentrations of total or virulent R equi in dams of foals with R equi-associated pneumonia were not significantly different. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that dams of foals with R equi-associated pneumonia did not shed more R equi in feces than dams of unaffected foals; therefore, R equi infection in foals was not associated with comparatively greater fecal shedding by their dams. However, detection of virulent R equi in the feces of all mares during at least 1 time point suggests that mares can be an important source of R equi for the surrounding environment.